N-dodecane Hydroisomerization Research Articles

Effect of Fe substitution over ZSM-48 on performance of n-dodecane hydroisomerization and distribution of isomers

A series of Fe substituted ZSM-48 nanocrystal aggregates were synthesized by the dynamic hydrothermal method. Through incorporation of Fe into ZSM-48 framework, the acidity of ZSM-48 zeolites has been modified. The hydroisomerization performances of n-dodecane were investigated on Pt supported ZSM-48 and Fe incorporated ZSM-48 zeolites. Fe incorporated ZSM-48 catalysts show higher n-C12 hydroisomerization selectivity compared with parent sample due to weaker acid strength of Si–OH–Fe than Si–OH–Al. High temperature favor the generation of the multi-branched isomers (mainly dimethyl isomers) following the “Key-Lock” mode. Meanwhile, 5-methylundecane is the main product in the monomethyl isomers (MOB) and 2,6-dimethyldecane is the main product in the multi-branched isomers (MUB), which suggests the excellent shape selectivity of ZSM-48 and the “Key-Lock” mode is preferred on ZSM-48 catalysts regardless Fe substituted or not. The relationship between the mono-methyl isomers and the butene-TPD results has been correlated and investigated. Four desorption peaks corresponding to butene weakly adsorbed over Si–OH, Fe–OH or Lewis acid sites, the “Key-Lock” mode adsorbed butene, the “Pore-Mouth” mode adsorbed butene and the strongly adsorbed butene respectively, can be distinguished. ZLC results indicate that Fe modified ZSM-48 can effectively increase n-hexane diffusion rate and reduce the activation energy of diffusion of n-hexane, which is benefit for the hydroisomerization performance. SMOB/SMUB can be altered by Fe modification, however, the distribution of the mono-methyl isomers can hardly be affected.

Mercaptoamine-assisted Post-encapsulation of Metal Nanoparticles within Preformed Zeolites and their Analogues for Hydroisomerization and Methane Decomposition.

We report a general synthetic strategy for post-encapsulation of metal nanoparticles within preformed zeolites using post-synthetic modification. Both anionic and cationic precursors to metal nanoparticle are supported on 8- and 10-membered ring zeolites and analogues during wet impregnation using 2-aminoethanethiol (AET) as a bi-grafting agent. Thiol groups are coordinated to metal centers, whereas amine moieties are dynamically attached to micropore walls via acid-base interactions. The dynamic acid-base interactions cause the even distribution of the metal-AET complex throughout the zeolite matrix. These processes encapsulate Au, Rh, and Ni precursors within the CHA, *MRE, MFI zeolite, and SAPO-34 zeolite analogues, for which small channel apertures preclude the post-synthesis impregnation of metal precursors. Sequential activation forms small and uniform nanoparticles (1-2.5 nm in diameter), as confirmed through electron microscopy and X-ray absorption spectroscopy. Containment within the small micropores protected the nanoparticles against harsh thermal sintering conditions and prevented the fouling of the metal surface by coke, thus resulting in a high catalytic performance in n-dodecane hydroisomerization and methane decomposition. The remarkable specificity of the thiol to metal precursors and the dynamic acid-base interaction make these protocols extendable to various metal-zeolite systems, suitable for shape-selective catalysts in challenging chemical environments.

Superior activity and isomerization selectivity in n-dodecane hydroisomerization over Ni clusters on ZSM-22 zeolite with structural defects

Developing nonnoble catalysts with high performance for the selective hydroisomerization of long-chain n-alkanes to isoalkanes that are comparable to commercial Pt catalysts is important but challenging. We report a low-loading nickel catalyst on structure-defective nanosized ZSM-22 zeolite (Ni/SD-HZSM-22, 1.0 wt%) with superior activity and isomerization selectivity for n-dodecane hydroisomerization than a commercial Pt catalyst (Pt, 0.5 wt%). The developed Ni/SD-HZSM-22 catalyst achieves 86.0–88.6 % n-dodecane conversion and 80.0–81.3 % C12-isomer yield, outperforming the conventional ZSM-22–supported Ni catalyst (Ni/HZSM-22; 50.4 % and 41.1 %, respectively) and the commercial Pt catalyst (56.8 % and 52.4 %, respectively) under the same reaction conditions, with high durability for 120 h. This is because SD-HZSM-22 with abundant surface structural defects increased available 10-membered ring openings, anchoring the small-sized Ni species and enhancing the isomerization activity and selectivity, endowing Ni/SD-HZSM-22 with good synergy between metal and acid functions.

Preparation of ZSM-22/ASA composite material for enhancing n-dodecane hydroisomerization performance

The ZSM-22/ASA composite material for efficient hydroisomerization of n-dodecane was successfully prepared via a two-step synthesis method. The structure, pore properties, and acidity of the catalysts were elucidated by the means of XRD, N2 physical adsorption, TEM, FT-IR, and Py-IR. Compared with the mixture catalyst, ZSM-22/ASA has a higher average pore diameter and formed a uniform and open channel structure, which is favorable to the diffusion of the reactant and the efficiency of the acid sites. The zeolite and the ASA phase in the composite are closely bonded by the interface effect, forming an additional Si–O–Al structure, which significantly affected the acidity of the composite catalyst. ZSM-22/ASA composite material exhibits enhanced n-dodecane hydroisomerization selectivity of total isomers and multi-branched isomers, which is attributed to its proper acid strength and pore structure conducive to diffusion. Finally, the location distribution of branched methyl groups was discussed and enhanced more central branching iso-dodecanes was obtained over the ZSM-22/ASA composite material.

Influence of W loading, support type, and preparation method on the performance of zirconia or alumina-supported Pt catalysts for n-dodecane hydroisomerization

Catalysts based on zirconia and alumina-supported tungsten oxides (3–18 wt% W) with a small loading of platinum (0.3 wt% Pt) were selected to study the influence of W loading, support type, and preparation methods on the hydroisomerization of n-dodecane. The alumina- and zirconia-supported catalysts show different catalytic properties that play an important role in n-dodecane conversion. Specific surface area and acidity of the alumina-supported catalysts are clearly higher than those of zirconia-supported counterparts. The 15 wt% W loaded catalysts were found to exhibit the best catalytic performance for the hydroisomerization of n-dodecane for both zirconia and alumina (67% of n-C12 conversion and 87% of i-C12 selectivity) based catalysts. Catalysts prepared by a single-step wet impregnation method were more active in the hydroisomerization of n-dodecane than catalysts prepared via several consecutive steps.

Fe-Substituted Pt/HZSM-48 for Superior Selectivity of i-C12 in n-Dodecane Hydroisomerization

Fe-Substituted Pt/HZSM-48 for Superior Selectivity of <i>i</i>-C₁₂ in <i>n</i>-Dodecane Hydroisomerization

Designed synthesis of single-crystalline silicoaluminophosphate zeolite via interzeolite transformation for n-dodecane hydroisomerization

Single-crystalline zeolites are highly desirable in this field owing to their high hydrothermal stability and high mass transfer efficiency. However, the preparation of single-crystalline silicoaluminophosphate SAPO-11 zeolite remains a significant challenge due to its complex synthesis process. Herein, we firstly report a facile and direct approach to synthesize single-crystalline SAPO-11 by interzeolite transformation via a kinetic-modulated process. The crystallization process of single-crystalline SAPO-11 was monitored by the time-dependent characterizations. A panel of characterizations by XRD, SEM, N 2 -adsorption and solid-state NMR provided evidence that the formation mechanism of single-crystalline SAPO-11 involved fast interzeolite transition process between two different topologies from AlPO 4 -8 (AET) to SAPO-11(AEL), thus it avoids the aggregation of small nanocrystals during the conventional polycrystalline SAPO-11 synthesis. In addition, the Brønsted acid sites of the prepared samples could be precisely regulated. The resulting single-crystalline catalyst exhibits superior isomer selectivity (92.3% vs. 70.6%) and yield (77.9% vs. 62.3%) in the n -dodecane hydroisomerization compared with the conventional polycrystalline sample due to the unique morphology and suitable acidity. This synthetic strategy provides a new orientation to design other single-crystalline zeolite catalysts. Single-crystalline SAPO-11 molecular sieve is synthesized through interzeolite transformation mechanism and has outstanding catalytic performance for the hydroisomerization of n -dodecane. • A new strategy to prepare a single-crystalline SAPO-11 by interzeolite transformation under kinetic-modulated process. • A clear recognition for the formation mechanism involved interzeolite transition process from AlPO 4 -8 to SAPO-11. • The acidity of single-crystalline SAPO-11 could be precisely regulated. • The Pt/S-SAPO-11 catalysts exhibit excellent catalytic performance for the hydroisomerization of n -dodecane.

Superior Activity and Isomerization Selectivity of Structural Defects on Nanosized Zsm-22-Assisted Ni Clusters Compared with Commercial Pt Catalysts in N-Dodecane Hydroisomerization

Superior Activity and Isomerization Selectivity of Structural Defects on Nanosized Zsm-22-Assisted Ni Clusters Compared with Commercial Pt Catalysts in N-Dodecane Hydroisomerization

Pt@SAPO-11 bifunctional catalysts with spatial architecture constructed via a seed-directed solvent-free strategy for n-dodecane hydroisomerization

Inferior sintering-resistance of metal nanoparticles is an obstacle restricting the development of bifunctional catalysts in chemical industry. The construction of spatial architecture in zeolitic framework can enhance the stability of metal nanoparticles and prolong the service life of catalysts. A seed-directed solvent-free strategy was proposed here to prepare a metal-confined catalyst along the zeolitic framework to sterically encapsulate metal nanoparticles. The use of raw materials without extra solvents could improve synthetic efficiency of each kettle, reduce economic cost and decrease environmental pollution caused by organic solvents. The status of metal species was observed by aberration-corrected TEM images and XPS spectra, and the intracrystalline Pt species were speculated to isomorphically substitute the framework Al and P or occupy tens of micropore to form structural defect sites, leading to a decrease in the support acidity and a better balanced bifunctionality. While enhancing the metal stability, the maximum yield of isomer products was increased to 75% versus 63% for the conventional specimen synthesized by hydrothermal and post-impregnated method on n-dodecane hydroisomerization. The results provide an efficient route to the synthesis of alternative bifunctional catalysts for n-alkanes hydroisomerization, and promote the high value-added conversion of downstream products in coal/natural gas chemical industry.

Fe Incorporated Zsm-48 Nanocrystal Aggregates for N-Dodecane Hydroisomerization

Fe Incorporated Zsm-48 Nanocrystal Aggregates for N-Dodecane Hydroisomerization

Comparison of n-Dodecane Hydroisomerization Performance Over Pt Supported ZSM-48 and ZSM-22

ZSM-48 and ZSM-22 zeolites with similar Si/Al ratio were synthesized and modified by alkali treatment. Moreover, n-dodecane hydroisomerization performance of Pt supported ZSM-22 and ZSM-48 were investigated. The catalytic results showed that the activity and the isomers selectivity of n-dodecane hydroisomerization could be improved by alkali treatment. The isomers distributions were distinct for Pt/ZSM-48 and Pt/ZSM-22. Mono-branched isomers near the end of the chains were more prone to be generated on Pt/ZSM-22 catalyst, which suggested “pore-mouth” catalysis model dominating the hydroisomerization catalysis. However, di-branched isomers and mono-branched isomers with methyl near the middle of the carbon chains were favorable to be formed over Pt/ZSM-48 catalyst according to the “key-lock” catalysis model. Moreover, more central-branched isomers were formed at high reaction temperature (> 320 °C) especially for Pt/ HZSM-22.

Influence of the Reduction Temperature and the Nature of the Support on the Performance of Zirconia and Alumina-Supported Pt Catalysts for n-Dodecane Hydroisomerization

Catalysts based on zirconia- and alumina-supported tungsten oxides (15 wt % W) with a small loading of platinum (0.3 wt % Pt) were selected to study the influence of the reduction temperature and the nature of the support on the hydroisomerization of n-dodecane. The reduction temperature has a major influence on metal dispersion, which impacts the catalytic activity. In addition, alumina and zirconia supports show different catalytic properties (mainly acid site strength and surface area), which play an important role in the conversion. The NH3-TPD profiles indicate that the acidity in alumina-based catalysts is clearly higher than that in their zirconia counterparts; this acidity can be attributed to a stronger interaction of the WOx species with alumina. The PtW/Al catalyst was found to exhibit the best catalytic performance for the hydroisomerization of n-dodecane based on its higher acidity, which was ascribed to its larger surface area relative to that of its zirconia counterparts. The selectivity for different hydrocarbons (C7–10, C11 and i-C12) was very similar for all the catalysts studied, with branched C12 hydrocarbons being the main products obtained (~80%). The temperature of 350 °C was clearly the best reduction temperature for all the catalysts studied in a trickled-bed-mode reactor.

Influence of W Loading, Support Type, and Preparation Method on the Performance of Zirconia or Alumina-Supported Pt Catalysts for N-Dodecane Hydroisomerization

Influence of W Loading, Support Type, and Preparation Method on the Performance of Zirconia or Alumina-Supported Pt Catalysts for N-Dodecane Hydroisomerization

Design of Pt/SAPO-11 bifunctional catalyst with superior metal–acid balance constructed via a novel one-step pre-loading strategy for enhancing n-dodecane hydroisomerization performance

This novel pre-loading method is a simple method for the design of bifunctional catalysts with high product yield, which exhibits superior metal–support balance, liquid yield of 99% and isomer yield of 84% on n-dodecane hydroisomerization.

N-dodecane hydroisomerization over Pt/ZSM-22: Controllable microporous Brönsted acidity distribution and shape-selectivity

The controllable acidity distribution in micropore for ZSM-22 zeolites is successfully tailored by using a new template protective NH4+ exchange strategy. The location and density of microporous Brönsted acidity is tailored by controlling the degree of detemplation and the concentration of NH4+ aqueous solution, respectively. The distribution of microporous Brönsted acidity of these Pt/ZSM-22 catalysts obviously affects the shape-selectivity in the hydroisomerization of n-dodecane. Weak microporous acidity leads to the formation of centrally mono-branched isomers, while strong microporous Brönsted acidity near the pore mouth favors the formation of multi-branched isomers, and strong microporous Brönsted acidity deep inside the pore mouth favors cracking through (s, p) β-scission. By selectively tailoring microporous Brönsted acidity near the pore mouth with lower acid density, the isomer yield over Pt/ZSM-22 was increased from 40.7% to 63.7%. This enhanced catalytic performance comes from the preferable formation of centrally mono-branched isomers and multi-branched isomers through key-lock model.

Design and synthesis of Pt/ZSM-22 catalysts for selective formation of iso-Dodecane with branched chain at more central positions from n-Dodecane hydroisomerization

The formation of centrally branched iso-dodecane was controlled by absorption modes of alkene intermediates on ZSM-22, which included pore mouth type and key lock type. In this paper, we have designed and synthesized two kinds of ZSM-22 catalysts for selective formation of iso-dodecane with branched chain at more central positions from n-dodecane hydroisomerization. Aluminosilicate ZSM-22 was modified via carbonization of template to block the micropores and borosilicate ZSM-22 was synthesized. The characterization results and performance evaluation validated that micropore blockage could limit the pore mouth type at low reaction temperatures which favored the formation of iso-dodecane with side chain near the end of the carbon chain. Owing to the weak acid strength, higher temperatures, which favored the key lock mode, were needed to run the n-dodecane hydroisomerization over Pt/borosilicate ZSM-22. Both the two strategies for catalyst design achieved key lock adsorption mode and improvement of the selectivity for centrally branched iso-dodecane. Most importantly, weak acid sites on borosilicate ZSM-22 could catalyze double-bond isomerization reactions, which enhanced centrally branched iso-dodecane distribution up to more than 47%. Our research provides a prospective strategy for selective formation of centrally branched iso-alkanes and Pt/borosilicate ZSM-22 is expected to have potential applications in n-alkane hydroisomerization.

Effects of Pt site distributions on the catalytic performance of Pt/SAPO-11 for n-dodecane hydroisomerization

A series Pt/SAPO-11 were prepared by using incipient wetness impregnation (IWI) and colloidal impregnation (CI) methods. TEM, STEM, CO-FTIR and H2 chemisorption were employed to study the effects of preparation method on the distributions of Pt sites. The catalytic performance of Pt/SAPO-11 was evaluated by using n-dodecane as the model reactant in a fixed-bed reactor. The characterization results suggested that the Pt sites on IWI catalyst could be mainly distributed near the micropore mouth of SAPO-11, while the Pt sites on CI catalyst could be mainly distributed on the external surface. In n-dodecane hydroisomerization, IWI catalyst showed higher activity and isomerization selectivity than CI catalyst. Possible relationships between the distributions of Pt sites and the catalytic performance of Pt/SAPO-11 were discussed.

Enhanced n-dodecane hydroisomerization performance by tailoring acid sites on bifunctional Pt/ZSM-22 via alkaline treatment

Acidity controlled Pt/ZSM-22 catalysts for n-dodecane hydroisomerization were explored through a simple and efficient post-treatment with different NaOH concentrations, and then the resulting samples were characterized.

Micropore blocked core–shell ZSM-22 designed via epitaxial growth with enhanced shape selectivity and high n-dodecane hydroisomerization performance

Core–shell ZSM-22 designed via epitaxy and modified via micropore blockage exhibits high n-dodecane hydroisomerization performance.

High selectivity for n-dodecane hydroisomerization over highly siliceous ZSM-22 with low Pt loading

Pt/siliceous ZSM-22 with silanol nests exhibits high isomer selectivity with low Pt loading.